Kalamos head  is a massive domed volcanic intrusion.  The layered pattern on the rock is known as flow layering and is due to the sorting of crystals, at the time of solidification, into crystal rich and crystal poor layers.  This results in layers of different hardness, which then erode at different rates.

Overall, the rock is quite hard and the layers make for excellent handholds for climbing up, then jumping off.  See Erin back flipping off Kalamos.